The IP multimedia subsystem (IMS/MMD) is a standard established by the third generation partnership project (3GPP/3GPP2) for rapidly providing and deploying various multimedia services. One of the important features of the IP multimedia subsystem is to use the session initiation protocol (SIP) as a calling and signaling control function.
The SIP-based conference framework is an important function for the IP multimedia subsystem. The conference function is achieved between conference participants and a conference server through the SIP and the SIP-based protocol.
A user in a conference generally needs to send a file to all the other users or a part of the users in the conference, and the users who received the file may accept or refuse the file in the conference window. The flow for transferring a file to a user is described as follows: a file sender requests to make a session with a file receiver, negotiates to establish a file transmission channel, such as a message session relay protocol (MSRP) channel, between the file sender and the file receiver in the session, sends the file to the file receiver through the established file transmission channel, and terminates the file transmission channel when the file transmission is finished. The process for transferring a file to more than one user is described as follows: a file sender requests to make a session with a conference server and negotiates to establish a file transmission channel, such as a MSRP channel, between the file sender and the conference server in the session; the conference server requests to make a session with each file receiver respectively, and negotiates to establish a file transmission channel, such as a MSRP channel, between the conference server and each file receiver in the session; the file sender sends the file to the conference server through the established file transmission channel; and then the conference server sends the file to the file receivers, and terminates the file transmission channels between the file sender and the conference server and between the conference server and the file receivers when the file transmission is finished.
It can be seen from the above descriptions that, since a user in a conference sends a file to the other users in the conference through a file transmission session independent of the conference session, and the file sender would not send the conference information to the file receivers, the file receivers cannot get to know the association between the file and the conference, when receiving the file. In actual applications, if the file is associated with the conference, the file receiver generally needs to know the conference information associated with the file upon receiving the file, so as to facilitate the subsequent processing.